A massive quantity of carbon is available in the atmosphere in the form of carbon dioxide. Within the past 150 years, the concentration of carbon dioxide in the atmosphere has increased substantially. Whatever the cause, atmospheric carbon dioxide could be an economical, industrially viable and successful source of fuel, food, building materials and the like if combined with other constituents. One way of processing atmospheric carbon dioxide is to capture it through photosynthesis. Algae is one medium through which photosynthesis can be put to use.
Algae has many advantages over other plants. Plants as used herein include organisms capable of performing or facilitating photosynthesis. Advantages of algae include fast growth, high sequestration of solar energy, ease of processing and good nutrition. Over the last two decades, algae has become a popular focus of research for engineers and scientists. Various aspects of algae have been studied. For instance, algae can be used as a food substitute, a medium for carbon sequestration, an agent for generating oils and converting the oils into biodiesels for use as an energy source.
Therefore, it is important for scholars, researchers and producers to quickly cultivate massive quantities of algae to serve as a raw material for further processing. Algae cultivation is often the bottleneck for producing products on a viable or economic scale. Algae cultivation requires sufficient light, carbon dioxide and nutrients. Sunlight and carbon dioxide are in abundance. However, efficient and effective delivery of light, carbon dioxide and nutrients to a substantial quantity of growing algae cells is tricky.
One popular and relatively inexpensive location for cultivating algae is in ponds or reservoirs. Ponds and reservoirs can be of any size; large ponds could be a source of large quantities of algae. However, to effectively use light energy in a pond cultivation process, light must reach the cells of the algae. Cultivation ponds suffer from several drawbacks. As algae grows at the surface of cultivation ponds, newly formed algae creates a barrier to and throws a shadow on other algae found slightly lower in the medium. Carbon dioxide is captured by the top layers of the algae and a decreasing concentration of carbon dioxide is available for algae growing deeper in the medium.
Over the years, many systems and devices have been proposed to overcome these and other limitations associated with algae ponds. For example, transparent tubes and open-air circulation troughs have been proposed to more efficiently expose algae to light. Other solutions have suggested the use of jets, paddle wheels, etc. to circulate the growth medium (e.g., water) or to circulate the algae in container (e.g., ponds, troughs, tubes). However, nearly all of these inventions are prohibitively expensive or are incapable of producing relatively large quantities of algae. One problem with these systems is that jets and other components are too vigorous for most forms of algae because algae is relatively fragile. Algae does not contain or require substantial amounts of cellulosic fibers that are necessary to support non-aqueous plants such as trees and land-based crops. Another problem associated with efficient circulation is that mechanical energy input into the system is quickly damped and circulation is thwarted. Pond photosynthesis reactors have been used at various stages in algae cultivation. Photosynthesis occurs near the surface of the reactors. Growth is initially fast, but growth rapidly declines over time. One reason is that sunlight fails to reach more than about one-half inch of the algae in the water in stagnate or circulated algae ponds. Further, algae tends to sink as it grows.
Canal style photosynthesis reactors have been proposed as an improvement over ponds. In a canal type photosynthesis reactor, the cultivation liquid is flowing, and a turbulent current produced between the fluid and the channel walls can provide effective mixing or agitation of the cultivation liquid (medium) and suspended algae cells. Thus, a cell growth curve of a general channel type photosynthesis reactor shows much better results for canal type photosynthesis reactors as compared to pools or ponds. However, both pond and canal style reactors suffer some disadvantages such as a propensity for contamination by other organisms, dust and other pollutants.
These and other disadvantages can be overcome with the teachings provided herein.